The Wilms' tumor gene WT1 was isolated as a gene associated with tumorigenesis in Wilms' tumor, which is a pediatric renal tumor (see nonpatent literature 1). This gene encodes a zinc finger transcription factor associated with the regulatory mechanism of cell growth and differentiation, and apoptosis and tissue development.
The WT1 gene was originally classified as a tumor suppressor gene. However, based on the recent evidences shown in the following (i) to (iii):
(i) high expression of the wild-type WT1 gene in various human malignant tumors and solid cancers including hematopoietic malignant tumors such as leukemia and myelodysplastic syndromes (MDS),
(ii) growth inhibition of human leukemia cells and solid cancer cells treated by WT1 antisense oligonucleotides, and
(iii) growth promotion and differentiation inhibition of mouse myeloid precursor cells by constitutive expression of the wild-type WT1 gene,
it is suggested that the wild-type WT1 gene exhibits an oncogenic effect rather than a tumor suppressive effect on various malignant diseases (see patent literature 1).
There is also known high expression of the WT1 gene in solid cancers, such as gastric cancer, colon cancer, lung cancer, breast cancer, germ cell cancer, hepatic cancer, skin cancer, bladder cancer, prostate cancer, uterine cancer, cervical cancer and ovarian cancer (see patent literature 2).
In general, the immune system for eliminating foreign substances comprises humoral immunity, in which macrophages, which recognize an antigen and serve as antigen presenting cells, helper T cells, which recognize the antigen presented by the macrophages and produce various lymphokines to activate other T cells, and B lymphocytes, which differentiate into antibody producing cells via the actions of the lymphokines, are involved; and cell-mediated immunity, in which cytotoxic T lymphocytes (CTLs), which are produced through differentiation in response to antigen presentation, attack and destroy target cells.
Currently, it has been considered that cancer immunity is mainly based on cell-mediated immunity in which CTLs are involved. In the CTL-based cancer immunity, precursor T cells recognize a cancer antigen presented in the form of a complex of a major histocompatibility complex (MHC) class I and the cancer antigen, and thereby differentiate and grow into CTLs, which attack and destroy cancer cells. In this case, the cancer cell presents, on the cell surface, a complex of the MHC class I antigen and the cancer antigen, which is the target of the CTLs (see nonpatent literatures 2 to 5). MHC is called as a human leukocyte antigen (HLA) in humans.
It is considered that the above-mentioned cancer antigen, which is presented by an MHC class I antigen on the surfaces of cancer cells, i.e., target cells, is a peptide of about 8 to 12 amino acids produced through intracellular protease-mediated processing of an antigen protein synthesized in cancer cells (see nonpatent literatures 2 to 5). Currently, search for antigen proteins of various cancers is underway, but only a few proteins have been identified as a cancer specific antigen.
The present inventor synthesized polypeptides that each consist of 7 to 30 contiguous amino acids based on the amino acid sequence of the WT1 gene expression product and each contain at least one amino acid presumably serving as an anchor amino acid for binding with HLA-A*2402 or HLA-A*0201, confirmed that these peptides bind with HLA-A*2402 or HLA-A*0201 (these peptides are HLA-A*2402- or HLA-A*0201-restricted), and found that the binding of the peptides with HLA-A*2402 or HLA-A*0201 induces CTLs, resulting in cytotoxic response to target cells (hereinafter abbreviated as CTL response). From this fact, these peptides were identified as a CTL epitope derived from the WT1 gene expression product (WT protein).
At this point, WT1-specific CTL epitopes only for HLA-A*2402 and HLA-A*0201 (see patent literature 3), HLA-A*3303 (see patent literature 4) or HLA-A*1101 are identified (see patent literature 5). It is confirmed that CTL responses induced by the polypeptides disclosed by the above literatures are restricted by HLA-A*2402, HLA-A*0201, HLA-A*3303 and HLA-A*1101.
This indicates a possibility that the protein product of the tumor suppressor gene WT1 is a promising tumor rejection antigen, also called as a tumor associated antigen (TAA). In fact, high levels of WT1-specific CTLs or high-titer anti-WT1 antibodies were observed not in peripheral blood of healthy blood donors, but in that of cancer patients.
However, HLA types are diverse enough to serve as markers for identifying individuals. In the HLAs, MHC class I antigens are classified into HLA-A, HLA-B and HLA-C, and MHC class II antigens are classified into HLA-DP, HLA-DQ and HLA-DR. Each class has several types of antigens. The antigen binding site of each HLA has genetic polymorphism. For example, it is known that HLA-A, HLA-B and HLA-C have 27 or more, 59 or more, and 10 or more kinds of polymorphisms (alleles), respectively.
Therefore, there has been a desire to identify a cancer antigen that binds to other types of HLAs than HLA-A*2402, HLA-A*0201, HLA-A*3303 and HLA-A*1101 and induces a CTL response, and to thereby apply immunotherapy to a wider range of subjects.
Meanwhile, the following three of modified WT1 peptides were reported in two documents:
the WT1187P1Y peptide (YLGEQQYSV; SEQ ID NO: 12), the WT1126P1Y peptide (YMFPNAPYL; SEQ ID NO: 35) (see patent literature 6 for the above two peptides), and the WT1126P9M peptide (RMFPNAPYM; SEQ ID NO: 52) (see patent literature 7).
Further, the following two peptides were reported in the written argument for the examination of European patent No. 1127068: the WT1126P2L peptide (RLFPNAPYL; SEQ ID NO: 39) and the WT1126P2L&P9V peptide (RLFPNAPYV; SEQ ID NO: 75) (see nonpatent literature 7).
However, it has never been reported whether these WT1 modified peptides serve as a cancer antigen that binds to other types of HLAs than HLA-A*2402, HLA-A*0201, HLA-A*3303 and HLA-A*1101 and induces a CTL response.    Patent Literature 1: JP-A 9-104629    Patent Literature 2: JP-A 11-035484    Patent Literature 3: WO 00/06602 pamphlet    Patent Literature 4: Japanese Patent Application No. 2006-045287    Patent Literature 5: Japanese Patent Application No. 2006-355356    Patent Literature 6: WO 2005/053618 pamphlet    Patent Literature 7: WO 2007/016466 pamphlet    Non Patent Literature 1: Gessler, M. et al., Nature, vol. 343, pp. 774-778, 1990    Non Patent Literature 2: Cur. Opin. Immunol., vol. 5, p. 709, 1993    Non Patent Literature 3: Cur. Opin. Immunol., vol. 5, p. 719, 1993    Non Patent Literature 4: Cell, vol. 82, p. 13, 1995    Non Patent Literature 5: Immunol. Rev., vol. 146, p. 167, 1995    Non Patent Literature 6: Mol. Cell. Biol., vol. 11, p. 1707, 1991    Non Patent Literature 7: The written argument for the examination of European patent No. 1127068